Researchers say childhood asthma and obesity are both more common in the U.S. than they were a few decades ago. Although some studies have suggested that being overweight increases the risk of childhood asthma, few have looked at whether losing weight during childhood affects the risk of asthma.
“Our study indicates that high BMI [body mass index] during the first four years does not increase the risk of asthma at school age among children who have developed a normal weight by age 7 years,” write researcher Jessica Öhman Magnusson, MSc, of the Karolinska Institutet in Stockholm, Sweden, and colleagues in Pediatrics.
In the study, researchers looked at the relationship between BMI at ages 1, 1 1/2, 4, and 7 and asthma at age 8 in more than 2,000 Swedish children.
The results showed that children who had a high BMI at ages 1, 4, or 7 were more likely to be diagnosed with asthma by age 8 than normal-weight children.
Children who were overweight at age 7 also had signs of a higher risk for allergies.
But overweight children who reached a normal weight by age 7 were no more likely to have asthma by age 8 than other children.
Researchers say there may be several biological explanations for the link between being overweight and asthma.
One explanation may involve the hormone leptin, which is derived from fat and found in higher amounts in people who are overweight. Previous studies have suggested that leptin may cause exaggerated inflammatory responses by the immune system, a key feature of asthma.